It is a technique for a drive apparatus for a liquid crystal display (hereinafter LC display) screen to generate a step-wise changing drive voltage which varies its values and changes its poralities responsive to a frame frequency.
It is also inevitable for a battery drive apparatus, like a wrist watch, to supply a relative large current at an initializing or starting stage of the operation of the LC display screen in order to charge up as promptly as possible. During a stable operation. However, it is desirable for the drive apparatus to supply a relative small current supply in order to reduce the power consumption.
In order to achieve such operation, a drive apparatus for a LC display screen usually includes a resistor circuit so as to supply a large current through a relative low value of a resistor (hereinafter referred to as a low resistor) at a starting stage of operation of a LC display and then change to supply a small current through a relative high value of a resistor (hereinafter referred to as a high resistor) during a stable term of an operation.
A conventional drive apparatus usually has a fixed duty ratio of the time for to changing the high power supply compared to the time for the low power supply, in order to drive a particular size of a LC display apparatus.
Accordingly, a conventional drive apparatus for a LC display is limited to single use in a particular condition. Consequently, it is impossible to change a drive power according to a size of a LC display screen.
In order to do so, for a conventional drive apparatus, it is necessary to change a frame frequency for a LC display screen or to mount an additional slit resistor element outside. Otherwise, an additional high drive power IC needs to be changed outside when a LC display is changed to a large size of a screen from a small one.
However, such conventional techniques have severe problems. When a frame frequency for a display is reduced in order to change a screen size of a LC display, noisy flickers appear on a LC display screen.
For example, in a case of a wrist watch, when a frame frequency is reduced extremely, such flikers appear on a screen.
It is also another problems to mount an additional slit resistor or a high power IC outside. In such a case, it causes to become a problem for a packaging space of a drive unit. And even if a space problem is cleared, it is inevitable to cost up of the total cost of a display apparatus.
Accordingly, an object of this invention is to provide an improved LC display drive apparatus which can programmably or freely change its drive power according to the screen size of the LC display apparatus.
It is also an object of this invention to provide an improved driver means for a LC display which can programmably set a time for a high power supply and a time for a low power supply.
It is further object of the invention to change freely a switching time between a high power supply and a low power supply without any additional mounting of resistors or ICs outside according to a screen size of a LC display.